thrust::exclusive_scan

Defined in thrust/scan.h

template<typename DerivedPolicy, typename InputIterator, typename OutputIterator, typename T, typename AssociativeOperator> OutputIterator thrust::exclusive_scan(const thrust::detail::execution_policy_base<DerivedPolicy> &exec, InputIterator first, InputIterator last, OutputIterator result, T init, AssociativeOperator binary_op)

exclusive_scan computes an exclusive prefix sum operation. The term ‘exclusive’ means that each result does not include the corresponding input operand in the partial sum. More precisely, init is assigned to *result and the value binary_op(init, *first) is assigned to *(result + 1), and so on. This version of the function requires both an associative operator and an initial value init. When the input and output sequences are the same, the scan is performed in-place.

Results are not deterministic for pseudo-associative operators (e.g., addition of floating-point types). Results for pseudo-associative operators may vary from run to run.

The algorithm’s execution is parallelized as determined by exec.

The following code snippet demonstrates how to use exclusive_scan to compute an in-place prefix sum using the thrust::host execution policy for parallelization:

#include <thrust/scan.h>
#include <thrust/functional.h>
#include <thrust/execution_policy.h>
...

int data[10] = {-5, 0, 2, -3, 2, 4, 0, -1, 2, 8};

thrust::maximum<int> binary_op;

thrust::exclusive_scan(thrust::host, data, data + 10, data, 1, binary_op); // in-place scan

// data is now {1, 1, 1, 2, 2, 2, 4, 4, 4, 4 }